Windows reserves typically 75% of the Memory for Hiberfil.sys . This is normally enough after compression but maybe less especially if you use memory tools. The way to change hiberfile size is as follows :

powercfg /h /size

To turn off Hibernate use the following command:
powercfg /h off

Turning off hibernate in Windows8+ is:
1) No fast startup so impact on boot time
2) No way to save data if the battery reaches critical levels.
3) No way to save data on Thermal conditions